This invention relates generally to gas turbine engines and more particularly to oil line fittings in such engines.
A gas turbine engine includes many components, such as bearings, gears and splines, which need to be lubricated during operation of the engine. Commonly, a gas turbine engine incorporates a self-contained, re-circulating sump oil system to provide lubrication for these components as well as for cooling purposes. Various oil lines are utilized to circulate the lubricant about the system. These oil lines are often exposed to high temperature, sonic velocity air flow which can be detrimental to the integrity of the lines. Furthermore, the high temperature air flow can cause thermally generated breakdown products (i.e., xe2x80x9ccokexe2x80x9d) to form in the oil lines, thus hindering the proper lubrication of the engine components.
To protect against coking, the oil lines typically comprise a double-walled configuration that provides adequate insulation from the high temperature air flow. However, the oil line fittings that connect the oil lines to other components such as the sump or bearing housing require another means of protection. Thus, the oil line fittings are commonly enclosed by an insulation blanket, which is composed of very light gage, high temperature steel sheets enclosing high temperature insulation material. The insulation blanket thus protects the oil line fitting from the high temperature air flow and assures proper lubrication to the engine.
A potential problem encountered by all fittings in a gas turbine engine is loosening of the fitting due to engine vibrations that occur during operation. In the case of oil line fittings, a full separation of the oil line could dump sufficient oil into the combustion chamber to cause an engine fire. One known approach to preventing undesired loosening of fittings is the use of safety wire. Safety wiring is the securing together of two or more parts with wire such that any tendency of a threaded part to loosen will be counteracted by an additional tightening of the wire. With an oil line fitting, the wire would need to be strung through holes in the fitting and secured by anchors welded to the bearing housing.
However, safety wiring is difficult to use with oil line fittings because there is limited access to such fittings and there is limited free space due to the use of the insulation blankets. Also, the use of safety wiring would require substantial modifications in that the wire holes would need to be drilled in the fittings and insulation blankets, and anchors would need to be welded to the appropriate structure. The wire holes in the insulation blanket would also reduce its insulating effectiveness.
Accordingly, there is a need for an approach to preventing loosening of fittings, particularly oil line fittings, that is easy to install in a confined space and does not require substantial modifications to the fitting.
The above-mentioned need is met by the present invention which provides a coupling assembly having a first coupling member, a second coupling member, and a coupling nut disposed over a portion of the second coupling member and threadingly engaging the first coupling member to retain the first and second coupling members together. An insulation blanket encloses the coupling nut, and a retention strip having a first end attached to an inner surface of the insulation blanket and a second end attached to the coupling nut is provided to prevent loosening of the coupling nut.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.